Roll camber

[OGR34]

Right now I'm trying to establish my front view swing arm (fsva) length for my SLA front suspension. fsva depends on roll camber which is given by the equation: roll camber = wheel camber angle/chassis roll angle. Easy to apply but I'm finding difficulty in determining what my wheel camber angle/chassis roll angle should be. Any suggestions?

 

[GregLocock]

That depends on what you want. If there was one ideal number everybody would use that. You might decide you'd like tot keep the outer tire square to the road or even leaning in a bit, for a circuit car, on crossplies, whereas the same car on radials you might not bother as much. But for a road car that implies excessive roll camber gain, which causes kickback through the steering on potholes due to gyroscopic precession.

Once you have decided on an ideal roll camber gain you'll find that it affects your track change in jounce, and the RCH. So you need to know what you want for those.



Cheers

Greg Locock


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[GregLocock]

On rereading your other threads, you seem to think you can design a front suspension in isolation to the rear suspension or the whole vehicle. That may be possible, but it certainly is not the way I've ever done it. If i am designing a suspension for one end of a car with the other axle retained then I spend a lot of time looking at the existing setup, and its positives and negatives, before designing a new suspension for the new end.

I can't go into details, but some suspensions I have worked on from day 1:

live rear axle with coil springs and watts ilo leaf springs

IRS ilo live rear axle with coil springs and watts

IRS ilo leaf springs

multilink lower arm ilo solid lower arm for SLA front suspension



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[OGR34]

Thanks for the reply. Sorry I'm not exactly sure what IRS and ilo mean can you explain? I'm not very familiar with these terms as I'm quite new to the automotive community so please bear with me.

Now regarding designing the front suspension in isolation to the rear, I am actually considering the positives and negatives of the rear. That being said, semi-trailing arms on the rear don't have many benefits which is why I am limiting the performance on the front in terms of camber change since the car is RWD. When I figure out the exact geometry of the rear through some measurements, hopefully I can figure out its dynamic characteristics and take them into consideration when designing the front. With a very limited budget I don't intend to add any anti sway bars nor do I intend to buy high end coil overs that are meant for the track as the car that I am working on is primarily for cruising purposes.

I'm still waiting for my project sponsor to get back to me so for the time being I'm trying to figure out what approach I should take to determine how much camber change I want compared to the rear as it will determine my front view swing arm (FSVA). I also want to implement some anti-dive so that the occupants have some reasonable comfort under hard braking. The thing is I am quite lost on how to choose my side view instant center (IC) which will determine my side view swing arm (SVSA) length. Both static FSVA and SVSA lengths are key constraints that I will need to determine my final geometry. Now I've been reading race car vehicle dynamics by Milliken and Milliken so essentially what I want to do is figure out what both my front views and side views will look like so I can combine them using his method to determine the inner pivot axis construction and the only thing stopping me currently is the confusion that I just described.

 

[GregLocock]

IRS=independent rear suspension. ilo=in lieu (place) of.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

If you're not planning to use a front antiroll bar, I would still encourage that you design it in. It can be omitted from the actual build if you want ... but if it turns out that it would be of benefit (which I suspect that it will), you are not up the creek without a paddle.

Need not be complex. Here is one of the simplest front antiroll bar linkages I can think of:

http://images.wrenchead.com/smartpages/partinfo_resize/moc/F001050.jpg

It's for a MacPherson, but you can get the idea. Item 14 is the front crossmember which also supports the steering rack (not shown). Lower control arm 9 is bolted to the ends of the crossmember with a long through-bolt and nut and a spacer between the bushes (not shown here). The same pivot bolt for the lower wishbone goes through the antiroll bar clamps 12 which clamp bushing 11 around the anitroll bar. Link 13 operates the end of the antiroll bar and attaches to the tab with a hole in it on the strut. In your case, that tab would likely be on the upper arm, but same idea.

As for your side view instant center (i.e. antidive) ... Here is an aftermarket suspension based on a Ford Mustang II (one of the few long-term merits of that car was that they had a compact front suspension design that lent itself to being built into hot rods, but I digress).

http://www.fulltiltstreetrods.com/STANGASS3pd.JPG

Note how the upper arm is mounted to the frame rail. The pivot rod for the upper arm is cross-bolted with two bolts going in from the top, which you can clearly see in that photo. Want to change the side-view instant center? Change the thickness of shims underneath the upper arm pivot point. Want to change the front-view instant center? Shim the front and rear attachment points unequally. Want to change the caster? Shift the whole upper arm fore-and-aft (if you use slotted holes, this is easy to do). Experiment as you wish.